"You know the magnitude of the conspiracy against my country," Chavez read from the letter. "Your criteria has been clear and explicit, we hope to continue with the strength of that support."
Chavez only read parts of the message, which was handed to his foreign minister in Caracas by Libyan Finance Minister Abdulhafid Zlitni. It was not immediately clear why such a high-level official had delivered the letter.
"Long live Muammar Gaddafi," Chavez said in a televised address before lashing out at Western powers for recognizing the rebel National Transition Council.
"NATO is an embarrassment," he said, sporting a newly close-shaved haircut to lessen the impact of hair loss from chemotherapy treatments for cancer.
"We do not recognize the pantomime of transition that violates and destroys the basis of international law."
Holding firm despite growing international isolation and crippling financial sanctions, Gaddafi has sought to play on potential divisions by calling on tribes and soldiers in rebel-controlled areas to rise up and free their cities.
The Venezuelan leader warmly received Gaddafi two years ago on a rare trip to the Americas, giving the Libyan a jewel-encrusted replica sword. Gaddafi gave him a large tent in return.
Miami`s Nuevo Herald newspaper ran a story on Monday saying Zlitni had come to Caracas to ask for Chavez`s help in getting around sanctions blocking Libya`s oil sales. The story cited unnamed Western intelligence sources.